Police have described grim scenes after the Colorado cinema shooting including finding the body of the youngest victim.
Officers choked back tears at a preliminary hearing for James Holmes, accused of killing 12 people and injuring at least 58 more at a midnight screening in Aurora, outside Denver, in July.
As relatives dabbed away tears with handkerchiefs in court, a first responder recalled finding the youngest victim of the shooting, a six-year-old girl, with no pulse amid the carnage.
Clips were also shown of security video in which Holmes could be seen entering the cinema with an electronic ticket bought on July 8.
The evidence emerged at the start of a week-long hearing to decide whether there is enough evidence for a full trial of the 25-year-old, accused of opening fire at the premiere of the Batman movie The Dark Knight Rises.
The Aurora massacre revived the perennial US debate over gun control - an issue re-ignited even more intensely by last month's shooting of 20 children at a Connecticut school.
Officer Justin Grizzle, a former paramedic, said he almost slipped in a "huge amount of blood" as he entered the cinema.
As ambulances struggled to cope with the scale of the slaughter, Grizzle described how he transported six critically ill victims in four trips to area hospitals.
"I realised later that as I was slowing to make turns, I could hear blood sloshing in the back of my car," Grizzle testified, choking back sobs.
One man sitting in the officer's car along with his stricken wife had to be restrained to keep from jumping out to go and look for the couple's daughter Veronica, who at six was the youngest victim.
Sergeant Gerald Jonsgaard, one of the first officers on the scene, described finding Veronica Moser-Sullivan shortly after midnight on July 20.
"She had been carried down from the top to the front of the theatre. I checked for a pulse. She was dead," he said, voice breaking. A colleague said he felt a pulse, but the child was declared dead on arrival in hospital.
Holmes, sporting dark brown hair and a full beard, was led into court in handcuffs at the hearing expected to uncover more details about the shooting.
Clad in dark red prison scrubs, Holmes - who had bright orange hair when he first appeared in court shortly after the shooting - stared straight ahead and talked to no one.
Aurora policeman Jason Oviatt told the court how he at first thought Holmes was another officer when he arrived with dozens of other police in response to 911 emergency calls about the shooting.
Holmes had his hands on the top of a white car at the back of the building, and as Oviatt approached, he realised something was wrong.
"As I got closer, the man was just standing there, not moving. The overall picture didn't match a police officer as I got closer," said Oviatt.
Holmes offered no resistance when he was ordered to put his hands up.
"He was completely compliant ... He was very relaxed, there weren't normal reactions to anything ... He was very detached," Oviatt said, adding: "He seemed to be out of it, and disoriented."
Witnesses said Holmes threw smoke bomb-type devices before opening fire randomly with weapons including an AR-15 military-style rifle, a 12-gauge shotgun and a pistol.
Prosecutors will build up their case that the shootings were a premeditated act of mass murder, while Holmes's lawyers may argue he is mentally unfit to stand trial.